Most carpets have some form of dimensional stability problems due to changes in temperature and humidity and also due, in some cases, to the lack of integrity from high traffic and heavy rolling stock etc. These problems are particularly acute when nylon is used as the primary pile layer since nylon absorbs moisture and expands up to approximately 6% of its weight. In many other ways, however, nylon is a preferred form of material for use in making carpet because of its durability and cost.
Typically nylon is used to make the pile of the carpet and it is tufted into a polypropylene primary backing to which it is bound by a predominantly latex binder applied to the underside of the backing.
The nylon pile tufted into the primary backing by itself is flexible and relatively stable, resisting buckling or wrinkling from atmospheric changes in moisture or temperature. However, this intermediate product does not have the stability, mass or tuft bind to be a carpet. It is a mere piece of textile. Typically, integrity is added to this primary backing by the addition of a latex binder to bind the tuft bundles left below the primary backing together to add weight, stability and durability to the backing. However, as soon as this is done, problems can arise because of fiber growth in the primary pile due to atmospheric changes in relative humidity and temperature, leading to increased stress on the carpet as a whole. This can result in wrinkling, buckles and delamination, and in heavy traffic zones, reduce carpet integrity.
As disclosed in U.S. Pat. No. 4,822,658, a method has been developed of installing a carpet through the use of a hook and loop system. The most economical form of such installation is the attachment of the carpet at the perimeter and along the seams. This is essentially a "free float system". It is therefore desirable in such a system to have a carpet of inherent dimensional stability and integrity, particularly under conditions of humidity changes and high traffic.
Attempts have been made to prevent the growing and distortion of some forms of carpet, especially carpet tiles or carpets of 6 feet width or less, by making it heavier and heavier and by locking the nylon of the pile into the backing more rigidly with more and more binder, adhesive or glue. Other attempts have been made to give greater dimensional stability to the carpet by putting fiberglass into the backing. While these attempts can create more dimensional stability, they do not completely satisfy the need for atmospheric stability and integrity for the great majority of carpets, particularly wide width carpets of greater than 6 feet. Most such carpets still require adhesion to the floor across substantially all of their underside, typically by gluing to maintain atmospheric stability and integrity. This construction thus makes it difficult to install a carpet in a "free-float" system, i.e. one in which the carpet is installed only along its perimeter and seams.
One approach to this problem has been to moisten the carpet during installation prior to securing the carpet to the floor, as described in U.S. Pat. No. 5,479,755, issued to Pacione on Jan. 2, 1996. Moistening is done to deliberately cause the carpet to expand and then the carpet is affixed in place by the hook and loop system. This approach, however, does not teach how to obtain a carpet which does not swell to begin with when the nylon pile fibres become wet.
Also since carpet piles can differ, since the required stability and strength of carpets varies widely depending upon the anticipated use, and since cost plays a part in an item like carpet which is supplied in very large volume, it is desirable to have a series of constructions which can be used to engineer a carpet to a desired stability according to predetermined criteria so as to meet the anticipated conditions of use and cost. It is helpful if such constructions are able to be selected as required to achieve a predetermined selected dimensional stability and level of required integrity.